A hot-swap power controller allows electronic components, such as circuit boards, to be added, removed, or replaced within a system without removing power from other electronic components in the system. An example of the use of a hot-swap power controller is in a server, where expansion cards may be added by inserting the cards into empty slots in the server. The cards have terminals that mate with terminals in the slot. The mated terminals pass information to and from the card as well as supply power to the card. Typical voltages supplied to the slot power terminals are 12 volts and 3.3 volts.
One or more power controller ICs selectively couple the 12 volt and 3.3 volt power supply voltages to the corresponding slot terminals based on whether certain conditions are met. For example, the power supply voltages should only be applied, or continue to be applied, to the slot terminals if: 1) there is a card inserted into the slot; 2) the supply voltages are at their proper levels; and 3) there is no fault condition, such as an over-current. Other conditions may apply.
Once the above conditions are met, the power controller IC couples power to the card and, in some cases, generates a “power-good” signal for application to a system processor that is used to convey that the output power to the card is satisfactory. The power-good signal indicates to the system processor that it is now okay to communicate with the card since it is powered up.
If the power controller is not enabled by the system processor, the power controller will issue a “power not good” signal, which is a deasserted power-good signal. Further, if a card is not inserted into an expansion slot, the power controller for that slot will not provide power to that slot, and will output a deasserted power-good signal. A deasserted power-good signal may also be a result of an overcurrent condition, an input undervoltage, or an over-temperature condition that caused the power controller to shut off power to the card or other equipment. Therefore, detecting a deasserted power-good signal on the power-good terminal of the power controller does not indicate whether or not the power is not good due to problems with the system.
In a hot-swap system, each power controller typically controls power to only a few devices, each device being associated with a separate channel of the power controller. The power controller must separately control the power to each replaceable module and detect the power status of each individual replaceable module. Some systems include many replaceable modules or the capability of using many replaceable modules, such as a server that has expansion slots for receiving hot-swap expansion cards. Therefore, a single system may have many power controllers IC, each operating independently and providing their own sets of status and power-good signals to one or more system processors. The system must figure out, from all the independent signals, whether the system is healthy and how to react to any flags indicating that the system is not healthy.
Designers of such systems find it complex and difficult to deal with all the signals generated by the various power controller ICs. The above problems are also applicable in many other situations not relating to cards in a slot.
It is desirable to simplify the determination in an electronic system incorporating power controllers that the power subsystem is operating satisfactorily.